1. Field of the Invention
The present invention relates to a method for data regeneration of protected data wherein, based on error correction, a sampling time or a sampling threshold may be provisionally shifted without having an error-corrected output signal exhibit inadmissibly high data rates.
2. Description of the Prior Art
By comparing a sampled data signal to a data signal not yet sampled, a control criterion may be acquired that serves for the phase or/and frequency readjustment of a clock generator. Such a phase detector is described in IEEE, Journal of Lightwave Technology, Vol. LT-3, No. 6, pages 1312 through 1314. For extremely high data rates, small differences in running time caused either by tolerances or by temperature changes in the modules employed lead to the fact that signals are not sampled at an ideal point-in-time. Likewise, temperature changes can shift the sampling threshold, so that an optimum distinction between, for example, two statuses no longer may be established. Above all, however, changes in the transmission pulse shape, influences of the transmission path, pulse distortions of the reception side and asymmetrical influences on the two logical statuses transmitted prevent the definition of an optimum sampling threshold and of an optimum sampling time.
An object of the invention is to specify a method for optimum data regeneration.
This object is achieved by the method recited in claim 1.
Advantageous developments are recited in the subclaims.
The method has the great advantage that, on the basis of the error correction, it allows the sampling time or/and the sampling threshold to be shifted provisionally without having the error-corrected output signal exhibit inadmissibly high data rates.
Just like the sampling time, the sampling threshold can be varied in order to determine an optimum decision threshold.
Accordingly, in an embodiment of the present invention, a method is provided for data regeneration which includes the steps of: acquiring a control criterion for a phase locked loop from a reception signal; generating a sampling clock signal; continuously monitoring a transmission error rate to control the phase locked loop; provisionally modifying a controlled phase shift of the sampling clock signal compared to the reception signal and, thus, the sampling time; and identifying and setting an optimum sampling time based on the transmission error rates measured at different sampling times.
In an embodiment of the method, the sampling time is set.
In an embodiment of the method, the sampling time is modified only within a predetermined range.
In an embodiment of the method, the sampling time is only modified until a predetermined error rate is measured.
In an embodiment of the method, a provisionally set, new sampling time is only retained when the error rate monitored for the new setting lies below the error rate of a preceding time interval.
In an embodiment of the method, following a modification of the sampling time in only one direction, a lasting, new rated position is set when the measured error rate becomes lower.
In an embodiment of the method, the optimum sampling time is identified from the measured error rates only after a modification of the sampling time in both directions and a resetting thereof is implemented.
In an embodiment of the method, the modification of the sampling time occurs by a predetermined amount.
In an embodiment of the method, the modification of the sampling time is limited to specific time spans.
In an embodiment, the method further includes the step of employing a plurality of interleaved codes for data protection, wherein the data regeneration at a reception side occurs in different processing paths and the transmission errors are separately identified, and wherein the sampling times are modified for only one of at least two data streams.
In an embodiment of the method, the sampling times are modified with the assistance of an adjustable delay element.
In an embodiment of the method, the sampling times are modified via a correction voltage supplied to a controllable oscillator of the phase locked loop.
In a further embodiment of the present invention, a method for data regeneration is provided which includes the steps of: acquiring a control criterion for a phase locked loop from an encoded reception signal; generating a sampling clock signal; continuously monitoring a transmission error rate to control the phase locked loop; provisionally modifying a decision threshold for the reception signal; and identifying and setting an optimum decision threshold based on the transmission error rates given different decision thresholds.
In an embodiment of the method, the decision threshold is set.
In an embodiment of the method, the decision threshold is modified only within a predetermined range.
In an embodiment of the method, the decision threshold is only modified until a predetermined error rate is measured.
In an embodiment of the method, a provisionally set, new decision threshold is retained only when the error rate identified for a new setting lies below the error rate of a preceding time interval.
In an embodiment of the method, following a modification of the decision threshold in only one direction, a lasting, new rated position is set when the measured error rate becomes lower.
In an embodiment of the method, the optimum decision threshold is identified from the measured error rates only after a modification of the decision threshold in both directions and a resetting thereof is implemented.
In an embodiment of the method, the modification of the decision threshold occurs by a predetermined amount.
In an embodiment of the method, the modification of the decision threshold is limited to specific time spans.
In an embodiment, the method further includes the step of employing a plurality of interleaved codes for data protection, wherein the data regeneration at a reception side occurs in different processing paths and the transmission error rates are separately identified, and wherein the decision threshold is modified for only one of at least two data streams.
When the identified error rate of the new sampling time set provisionally lies above the error rate of the preceding sampling time, the previously employed sampling time (or the previously employed sampling threshold) is initially retained and a shift of the sampling time in the other direction is provisionally implemented in order to identify the optimum sampling time.
It is also advantageous that the sampling time and the sampling threshold be adjusted only within a predetermined range. What is thereby assured is that the data regeneration still works even upon a malfunction of the control. Given interleaved error-correcting codes, the monitoring and readjustment of sampling time and sampling threshold can occur in different data paths, each of which are individually optimized. This parallel processing is also required for technological reasons given high data rates. The other data path can serve as comparison criterion. The ranges wherein the sampling time and the sampling threshold move can be determined from the previously measured error rate and from the error rate occurring during the change.
It is also meaningful that, given a newly formed connection, the ranges for readjustment of sampling time and sampling threshold, as well as the change rate, are initially selected greater than given a connection which already exists. It is advantageous in this method that no second data path need be provided, this serving only for determining the optimum sampling time and the optimum sampling threshold that are then transmitted on the actual data path. In this method, an optimum setting and data regeneration no longer can be achieved due to tolerances in the various data paths.
Additional features and advantages of the present invention are described in, and will be apparent from, the Detailed Description of the Preferred Embodiments and the Drawing.